The present invention relates to a device for tuning of a resonator, more specifically to a resonator comprising a resonator body where the shape of the body can be changed and thus change the resonance frequency.
Among high-frequency and microwave resonator structures, so-called dielectric resonators have recently become increasingly interesting as they offer e.g. the following advantages over conventional resonator structures: smaller circuit sizes, higher integration level, higher efficiency and lower cost of manufacture. Any element having a simple geometric shape made of a material having low dielectric losses and a high relative dielectric constant can be used as a high Q dielectric resonator. For reasons of manufacturing technique, the dielectric resonator is usually cylindrical, such as a cylindrical disc.
The resonance frequency of the dielectric resonator is primarily determined by the dimensions of the resonator body. Another factor affecting the resonance frequency is the environment of the resonator. The electric or magnetic field of the resonator and, thus, the resonance frequency can be intentionally affected by introducing a metal surface or any other conductive surface in the vicinity of the resonator. To adjust the resonance frequency of the dielectric resonator, a common practice is to adjust the distance between the conductive metal surface and the planar surface of the resonator. The adjusting mechanism may be e.g. an adjustment screw attached to the housing surrounding the resonator.
Alternatively, it is also possible to bring another dielectric body to the vicinity of the resonator body instead of a conductive adjustment body. One prior art design of this kind, based on dielectric plate adjustment is shown in FIG. 1.
In this kind of adjusting method, however, it is typical that the resonance frequency varies nonlinearly as a function of the adjusting distance. Due to the non-linearity and the steep slope of adjustment, accurate adjustment of the resonance frequency is difficult and demands great precision, particularly at the extreme ends of the control range.
Frequency adjustment is based on a highly accurate mechanical movement, the slope of adjustment also being steep. In principle, the length and thus the accuracy of the adjusting movement may be increased by reducing the size of the metallic or dielectric adjustment plane.
Due to the non-linearity of the above mentioned adjusting techniques, however, the achieved advantage is small, since the portion of the adjusting curve which is too steep or too flat either at the beginning or at the end of the adjusting movement can not be used. As a result, adjusting the resonance frequency of a dielectric resonator with these solutions sets very high demands on the frequency adjustment mechanism, which in turn, increases the material and production costs. In addition, as the mechanical movements of the frequency adjustment device must be made very small, adjustment will be slower.
In U.S. Pat. No. 5,703,548, by Sxc3xa4rkkxc3xa4, the above problems was solved by introducing a dielectric resonator comprising a plurality of dielectric adjustment planes. This results in improved linearity of frequency adjustment and a longer adjusting distance, which both improve the accuracy of adjustment.
In U.S. Pat. No. 4,459,570, by Delaballe et al., a similar problem has been solved by introducing a resonator having a dielectric constant of an adjustment plate with half the value of the dielectric constant of the resonator disc.
In U.S. Pat. No. 5,315,274, by Sxc3xa4rkkxc3xa4, where tuning of a resonance frequency is achieved by a dielectric resonator comprising two cylindrical discs positioned on top of each other, which are radially displaceable with respect to each other and thereby varying the shape of the resonator.
The basic idea of the invention is to utilise the linear part of the adjustment curve although the curve is steep, thus difficult to adjust and to keep stable.
The object of the invention is a dielectric resonator in which the resonance frequency can be adjusted more accurately than previously within the steep slope.
In accordance with the invention this object is achieved by an inventive dielectric resonator, comprising a dielectric resonator body, where the resonator body includes at least two resonant elements, wherein by altering the shape of the dielectric resonator body the resonance frequency of said dielectric resonator can be adjusted. The alteration of the shape of the resonant body is performed in such a way that said elements are in mechanical contact, through connecting means, in at least one location at any time. This contact may be established via an interconnecting element. The dielectric resonator body also comprise means for moving at least a first resonant element in relation to at least a second resonant element of the resonant body and thus altering the shape of said body. The movement is be performed by rotation of the first element around an axis.
The dielectric resonator body may further comprise connecting means for connecting said first and second element, and the rotation, of said first element, can cause a displacement of said first element, in relation to said second element, in a direction of the rotation axis.
The resonator may comprise additional means for adjustment of the displacement by means for mechanical guidance. These means for adjustment may be incorporated in the connecting means by which the resonating elements are in contact with each other in at least one location.
The resonating elements may also be circularly cylindrical, where the connecting means are implemented in a circular or part-circular path, having a centre at said rotation axis.
A first advantage with the present invention is that a maximal stability in respect of relative displacement and vibrations between the elements is achieved.
A second advantage is that a temperature compensating resonator structure easily can be implemented.
A third advantage is that a compact resonator structure is obtainable.
A fourth advantage is that a high sensitivity can be obtained in respect of resonance frequency versus displacement.
A fifth advantage is that this type of dielectric resonator body can operate in a high power environment.
In the following, the invention will be disclosed in greater detail by way of example with reference to the attached drawings.